This invention relates to weather radar and specifically for a weather radar capable of rapid detection and alerting of weather hazards.
Aviation weather hazards include the following: turbulence, hail, lightning, very high precipitation rates, low level windshear, and icing. Some of these hazards may be directly detected while others may be inferred by detecting the type of weather features they are associated with. Turbulence, hail, lightning, and very high rain rates are only associated with convective weather cells. Therefore separating the detection problem into detection of convective weather verses non-convective weather can be very useful. Low-level windshear and icing may be produced by both convective weather as well as other weather types such as stratiform or orthographic weather.
A detectable hazard may be present when the aircraft flight path intersects an area in and around a thunderstorm. Since the aircraft may be flying over a considerable altitude range and the thunderstorm may also exist over both an altitude range and a large extent of sampled azimuth space, the weather radar may be forced to scan over a substantial volume of space. Such volume scans are time consuming and are not compatible with the rapid update requirements needed in a dynamic aircraft environment. This time consuming volume scan generally forces the radar to support both detection and assessment of a hazard with the same sampled data. Therefore the radar may not be optimized for either detection or assessment but supports a compromised data set that provides suboptimal detection and suboptimal assessment.
Some current weather radar systems completely sample a volume of space in front of an aircraft to produce a three-dimensional display. Both horizontal and vertical radar displays are included in these systems. Data that drives the vertical display is built from three-dimensional data sampled from multiple azimuth scans at different antenna beam elevations. With the possible range of heights of weather features and with this data being desired at both moderate and short ranges, the range of vertical elevations that must be sampled produce very long update times. Storing the data in a position corrected memory and reading out the data as needed can improve the apparent latency experienced by the aircrew using this type of radar.
Aircraft heading changes produce new regions of space that must be quickly sampled to produce acceptable display latency. One way to quickly sample the new regions is to scan only those regions of space that are new and not to rescan those regions that have already been scanned. Regions of space that are not scanned are being turned away from. The antenna sweep is slowed in new regions of space that are in front of the aircraft due to the turn to improve estimates of reflectivity and turbulence. This method is disclosed in U.S. Pat. No. 6,512,476 titled “Adaptive Radar Scanning System” by Daniel L. Woodell and assigned to the assignee of the present invention and incorporated herein by reference.
The design of a volume scanning weather radar system is driven by a set of conflicting design goals listed below:                1. Low latency display versus a stable display        2. Low latency display versus a fully sampled volume        3. Ground clutter free display versus detection of all weather        4. Fast antenna sweep speed to support low latency volume detection versus slow sweep speed to dwell on long range targets for long range detection        5. High pulse rates to sample velocities versus low pulse rates to sample long ranges        6. Pulse patterns that reject targets at ambiguous ranges versus pulse patterns that allow the best detections        7. Pulse patterns that minimize clutter contamination versus pulse patterns that support detection of weak returns or the detection of the velocity of returns.        
A weather radar design is driven by the multiple tradeoffs of one design goal versus another. The previously described weather radar system in U.S. Pat. No. 6,512,476 trades latency for a full volume sampling process that allows the production of both a horizontal data display and vertical data display from the same three-dimensional data. In some cases, technology may be inserted to allow previously incompatible goals to be met at the same time. Such is the case with a weather radar disclosed in U.S. Pat. No. 6,424,288 “Multi-Sweep Method and System for Detecting and Displaying Weather Information on a Weather Radar System” by Daniel L. Woodell and assigned to the assignee of the present invention and incorporated herein by reference. In U.S. Pat. No. 6,424,288 multiple antenna beams allow antenna tilts optimized for long-range detection to be compatible with production of a ground clutter free display.
What is needed is an alternate mitigation strategy for the volume update problem that inserts new technology to allow timely sampling of both horizontal and vertical weather environments. Such a technology insertion should allow both weather detection and hazard assessment/characterization to be independently optimized.